I propose to add a fifth answer (as a third one) (&#39;TwoColorsOccur) to the exercise 5.1.5 to cover the following situtation:<br><br>(check-color &#39;blue &#39;red &#39;red &#39;blue) -&gt; &#39;TwoColorsOccur<br> [(and (symbol=? T1 G2) (symbol=? T2 G1)) &#39;TwoColorsOccur]<br>
<br>Under the current answers this situation would result in &#39;OneColorOccurs, which would be misleading...<br><br>Have a good day.<br><br>Jakub Hadam<br><br>